Electrical switch

ABSTRACT

An electrical switch having a casing, at least two fixed contacts and a corresponding moving contact. The moving contact has two parts contactable with the fixed contacts respectively thereby closing the switch. An operating member is supported for movement for moving the moving contact to close the switch. A spring acts upon the moving contact such that its two parts are inclined at an acute angle relative to the fixed contacts, with at least one of the parts being spaced apart from the corresponding fixed contact while the switch is open. The moving contact is movable such that said at least one or both of its parts comes or come into contact with the corresponding fixed contact or contacts against the action of the spring. In particular, the moving contact is movable against the action of the spring to have its two parts turning through said acute angle until both parts are in contact with the corresponding fixed contacts.

[0001] The present invention relates to a switch for controlling theoperation of an electrical appliance.

BACKGROUND OF THE INVENTION

[0002] The electrical switch of a known type includes a casing, twofixed contacts and a moving contact which has opposite ends forshort-circuiting the fixed contacts to close the switch upon movement byan operating member through the action of a spring. In case that thespring malfunctions and in particular when it is broken, the movingcontact may stay in contact with the fixed contacts. This situation isundesirable and not safe.

[0003] The invention seeks to mitigate or at least alleviate such aproblem by providing an improved electrical switch of this type ingeneral.

SUMMARY OF THE INVENTION

[0004] According to the invention, there is provided an electricalswitch comprising a casing, and at least two fixed contacts and acorresponding moving contact in the casing. The moving contact has twoparts contactable with the fixed contacts respectively thereby closingthe switch. An operating member is supported for movement relative tothe casing for moving the moving contact to close the switch. Resilientmeans acts upon the moving contact such that its two parts are inclinedat an acute angle relative to the fixed contacts, with at least one ofthe parts being spaced apart from the corresponding fixed contact whilethe switch is open. The moving contact is movable such that said atleast one or both of its parts comes or come into contact with thecorresponding fixed contact or contacts against the action of theresilient means.

[0005] Preferably, the moving contact has one side facing the fixedcontacts and an opposite side on which the resilient means is provided.

[0006] More preferably, the resilient means comprises a compression coilspring.

[0007] In a preferred embodiment, the electrical switch includes acarrier movable by the operating member and carrying the moving contactand the resilient means for simultaneous movement. The carrier includesan inclined portion lying against which the moving contact is acted uponby the resilient means to incline at said acute angle relative to thefixed contacts.

[0008] More preferably, the fixed contacts are spaced apart by a gap,and the carrier is supported for movement in the gap such that itsinclined portion is movable at least partially beyond the fixed contactsto allow the two parts of the moving contact to contact with thecorresponding fixed contacts.

[0009] More preferably, the carrier includes a recess having opposite,first and second ends and locating the moving contact and the resilientmeans. The moving contact lies against the first end that being theinclined portion and the resilient means co-acts between the movingcontact and the second end.

[0010] In a specific construction, the electrical switch includes twopairs of said fixed contacts and two corresponding said moving contactsmovable simultaneously by the operating member for operation.

[0011] In general, the electrical switch may include a sliding carriercarrying the moving contact and the resilient means for simultaneousmovement, a slider movable by the operating member for in turn movingthe carrier, and an over-centre pivotal spring co-acting between thecarrier and the slider such that the carrier and the slider are slidablein opposite directions.

[0012] Slightly more specifically, the operating member is supported forpivotal movement and is connected to the slider by means of a link formoving the slider.

[0013] The electrical switch may be a normally-open switch, in that theoperating member is resiliently biassed by a spring towards aninoperative position.

[0014] In particular, the electrical switch may be a trigger switch foruse in an electric power tool.

[0015] According to a slightly different aspect of the invention, thereis provided an electrical switch comprising a casing, and at least twofixed contacts and a corresponding moving contact in the casing. Themoving contact has two parts contactable with the fixed contactsrespectively thereby closing the switch. An operating member issupported for movement relative to the casing for moving the movingcontact to close the switch. The moving contact is supported with itstwo parts inclined at an acute angle relative to the fixed contactsunder the action of resilient means such that at least one of its partsis spaced apart from the corresponding fixed contact whale the switch isopen. The moving contact is movable against the action of the resilientmeans to have its two parts turning through said acute angle until bothparts are in contact with the corresponding fixed contacts.

BRIEF DESCRIPTION OF DRAWINGS

[0016] The invention will now be more particularly described, by way ofexample only, with reference to the accompanying drawings, in which:

[0017]FIG. 1 is a side view of an embodiment of an electrical switch inaccordance with the invention, said switch having a pair of movingcontacts and associated fixed contacts and an operating member foroperating the moving contacts;

[0018]FIG. 2 is a top plan view of the switch of FIG. 1;

[0019]FIG. 3 is an end view of the switch of FIG. 1;

[0020]FIG. 4 is a cross-sectional side view of the switch of FIG. 1,showing its internal construction;

[0021]FIG. 4A is a bottom plan view of part of the switch of FIG. 4,showing its moving and fixed contacts;

[0022]FIG. 5 is a bottom plan view of the switch of FIG. 4; and

[0023]FIG. 6 is a schematic circuit diagram showing the switch of FIG. 1connected to a load and a power source.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

[0024] Referring to the drawings, there is shown an electrical switch100 embodying the invention, which switch 100 has a rectangular casing110 and an operating trigger 120. The casing 110 has an invertedU-shaped cross-section that is closed by a bottom plate 119 such thatopposite, front and rear ends 118 of the casing 110 are open. The casing110 includes a top wall, on which a elongate integral support 111 liesthat projects beyond the front casing end 118. Two holes 114 areintegrally formed at a free end 112 of the support 111 for mounting theoverall switch 100 by means of screws for example.

[0025] The switch 100 is a normally-open switch and is designed to beused for trigger control in electric power tools, and in particular butnot exclusively heavy current, for example 25A, power tools such as acircular saw 10.

[0026] The support end 112 is crooked upwards to form a hinge 113 thatconnects the trigger 120 for pivotal movement. The trigger 120 is of aninverted U-shaped cross-section embracing the support end 112 and hinge113. The trigger 12(r has a top wall 121 for depression by a user andincludes a pair of opposed side walls 122 connected at its outer topcorner to the hinge 113. An internal compression coil spring 123 co-actsbetween the top wall 121 and the support end 112 for resilientlybiassing the trigger 120 to pivot upwardly into an inoperating position(solid line). Upon depression, the trigger 120 pivots downwardly into anoperating position (dotted line) against the action of the spring 123.The trigger 120 will return to the inoperating position upon release.

[0027] The trigger side walls 122 are also hinged, at its outer bottomcorner, to a linkage rod 124 that extends internally along the support111 back to above the switch casing 110. The support 111 houses, withinits rear end, a slider 115 that is articulated with the rear end of therod 124 for movement thereby in opposite directions upon depression andrelease of the trigger 120. The slider 115 is in engagement with acompression coil spring 116 underneath it.

[0028] Housed within the casing 110, the switch 100 includes two, frontand rear pairs of fixed contacts 130 and 135 and two corresponding pairsof moving contacts 140 and 145 arranged to make and break electricalconnection between the fixed contacts 130 and 135 of the correspondingpairs. Each pair of the moving contacts 140/145 is mounted on oppositeends of a corresponding transversely-extending contact bar 141/146,together acting effectively as a single moving contact. Each pair of thefixed contacts 130/135 and the associated moving contact(s) 140/145constitute an individual switch, and both switches are simultaneouslyoperable by the trigger 120.

[0029] The front fixed contacts 130 are mounted on the inner ends ofrespective identical S-shaped contact strips 131, whose outer ends arepositioned just within the front casing end 1 and act as a pair ofterminals 132. The rear fixed contacts 135 are mounted on the inner endsof respective identical U-shaped contact strips 136, whose outer endsare positioned just within the rear casing end 118 and act as anotherpair of terminals 137. The contact strips 131/136 of each pair arelaterally aligned and,run in parallel on opposite, left and right sideswithin a corresponding casing end 118, being spaced apart to form a gapG therebetween that extends along the central axis of the casing 110. Inparticular, the fixed contacts 130/135 of each pair lie on a planeperpendicular to the central axis.

[0030] Also housed within the casing 110, the switch 100 includes acarrier 150 which is supported for sliding movement in oppositedirections within the gap G and therealong. The carrier 150 ispositioned directly below the slider 115 and is in engagement with thecoil spring 116, with the spring 116 co-acting between the two sliders115 and 150. The spring 116 acts an over-centre pivot that pivots inopposite directions for expansion past a central position at which it iscompressed. Thus, upon movement of the slider 115 in one or the otherdirection by the rod 124, the carrier 150 is slid rapidly in theopposite direction by the spring 116 as a result of its re-expansion.

[0031] The carrier 150 includes, on its lower side, a pair of front andrear recesses 151 and 156 carrying the moving contact bars 141 and 146respectively for simultaneously movement. As shown in FIG. 4A, eachrecess 151/156 has a rear end wall 152/157 that is inclined laterally atan acute angle of 10° to 30° and includes a front end seat 153/158 thatlocates horizontally a respective compression coil spring 154/159. Thespring 154/159 points at the inclined end wall 152/157, between whichthe corresponding contact bar 141/146 is compressed. Thus, the movingcontacts 140/145 face the corresponding fixed contacts 130/135 on oneside and are acted upon by the spring 154/159 on the opposite side.

[0032] Each coil spring 154/159 urges the contact bar 141/146 to lieflat against the corresponding inclined end wall 152/157, such that thecontact bar 141/146 or the moving contacts 140/145 are normally inclinedat the same angle relative to the corresponding fixed contacts 130/135.This condition is shown in FIG. 4A, which corresponds to the inoperatingposition of the trigger 120 (solid line) and in which the movingcontacts 140/145 are inclined and thus spaced apart (on at least oneside as shown) from the fixed contacts 130/135.

[0033] Upon depression of the trigger 120 (dotted line), the carrier 150is slid via the rod 124, the slider 115 and the spring 116. In response,the carrier 150 moves the moving contacts 140/145 flat against thecorresponding fixed contacts 130/135 counteracting the springs 154/159,thereby closing the overall switch 100. The carrier 150 slides to moveits inclined walls 152/157 beyond, or at least partially beyond, thecorresponding fixed contacts 130/135, thereby allowing the movingcontacts 140/145 to engage the fixed contacts 130/135.

[0034] In particular, the moving contacts 140/145 will turn through theaforesaid acute angle about the moving contacts 140/145 on one side thatare in, or have earlier come into, engagement with the respective fixedcontacts 130/135 until the moving contacts 140/145 on the other side hitthe corresponding fixed contacts 130/135.

[0035] Upon release of the trigger 120, the switch 100 returnsautomatically to the normally-open condition.

[0036] The switch 100 is to be connected, using its terminals 132 and137, between the power tool 10 and an AC power source 20.

[0037] In the construction of this particular switch 100 as described,the operating trigger 120 acts through the springs 123 and 116. Theover-centre pivot spring 116 is especially prone to breaking throughrepeated operations. The moving contacts 140 and 145 are inclined at anacute angle, while lying against the inclined portions 152 and 157,relative to the fixed contacts 130 and 135 under the action of thesprings 154 and 159. Should the pivot spring 116 break, the contactsprings 154 and 159 in conjunction with the inclined portions 152 and157 will instantly cause the moving contacts 140 and 145 to turn awayfrom the fixed contacts 130 and 135, whereby the switch 100 is openedfor safety.

[0038] It is understood that the springs 154 and 159 may take any otherforms of resilient means, such as a spring lever or an elbow spring.

[0039] The invention has been given by way of example only, and variousother modifications of and/or alterations to the described embodimentmay be made by persons skilled in the art without departing from thescope of the invention as specified in the appended claims.

What is claimed is
 1. An electrical switch comprising a casing, at leasttwo fixed contacts and a corresponding moving contact in the casing, themoving contact having two parts contactable with the fixed contactsrespectively thereby closing the switch, an operating member supportedfor movement relative to the casing for moving the moving contact toclose the switch, and resilient means acting upon the moving contactsuch that its two parts are inclined at an acute angle relative to thefixed contacts, with at least one of the parts being spaced apart fromthe corresponding fixed contact while the switch is open, the movingcontact being movable such that said at least one or both of its partscomes or come into contact with the corresponding fixed contact orcontacts against the action of the resilient means.
 2. The electricalswitch as claimed in claim 1, wherein the moving contact has one sidefacing the fixed contacts and an opposite side on which the resilientmeans is provided.
 3. The electrical switch as claimed in claim 2,wherein the resilient means comprises a compression coil spring.
 4. Theelectrical switch as claimed in claim 1, including a carrier movable bythe operating member and carrying the moving contact and the resilientmeans for simultaneous movement, the carrier including an inclinedportion lying against which the moving contact is acted upon by theresilient means to incline at said acute angle relative to the fixedcontacts.
 5. The electrical switch as claimed in claim 4, wherein thefixed contacts are spaced apart by a gap, and the carrier is supportedfor movement in the gap such that its inclined portion is movable atleast partially beyond the fixed contacts to allow the two parts of themoving contact to contact with the corresponding fixed contacts.
 6. Theelectrical switch as claimed in claim 4, wherein the carrier includes arecess having opposite, first and second ends and locating the movingcontact and the resilient means, the moving contact lying against thefirst end that being the inclined portion and the resilient meansco-acting between the moving contact and the second end.
 7. Theelectrical switch as claimed in claim 1, including two pairs of saidfixed contacts and two corresponding said moving contacts movablesimultaneously by the operating member for operation.
 8. The electricalswitch as claimed in claim 1, including a sliding carrier carrying themoving contact and the resilient means for simultaneous movement, aslider movable by the operating member for in turn moving the carrier,and an over-centre pivotal spring co-acting between the carrier and theslider such that the carrier and the slider are slidable in oppositedirections.
 9. The electrical switch as claimed in claim 8, wherein theoperating member is supported for pivotal movement and is connected tothe slider by means of a link for moving the slider.
 10. The electricalswitch as claimed in claim 1, being a normally-open switch, wherein theoperating member is resiliently biassed by a spring towards aninoperative position.
 11. The electrical switch as claimed in claim 10,being a trigger switch for use in an electric power tool.
 12. Anelectrical switch comprising a casing, at least two fixed contacts and acorresponding moving contact in the casing, the moving contact havingtwo parts contactable with the fixed contacts respectively therebyclosing the switch, and an operating member supported for movementrelative to the casing for moving the moving contact to close theswitch, wherein the moving contact is supported with its two partsinclined at an acute angle relative to the fixed contacts under theaction of resilient means such that at least one of its parts is spacedapart from the corresponding fixed contact while the switch is open, andthe moving contact is movable against the action of the resilient meansto have its two parts turning through said acute angle until both partsare in contact with the corresponding fixed contacts.